1. Technical Field
This invention relates to controllers for groundwater sampling pumps, and more particularly to an electrical controller which controls the timing and duration of the injection of compressed air into a bladder within a bladder pump and the subsequent venting of the compressed gas in order control the rate at which fluid is pumped by the bladder pump.
2. Background Art
Fluid pumps such as bladder pumps are commonly used in the sampling of groundwater. A bladder pump commonly consists of a housing which forms a chamber, inside of which is an inflatable bladder. When the bladder is filled with compressed gas, fluid admitted to the housing inside the chamber is forced (i.e. squeezed) by the bladder up through a discharge tube within the housing and discharged from the top of the discharge tube. When the bladder is subsequently vented, the chamber is refilled as fluid from the ground is admitted into the chamber through a one-way valve at a bottom fluid inlet of the pump and held within the chamber until the bladder is again filled with compressed gas and the fluid is discharged. A complete pump cycle therefore includes a refill and a discharge operation. Normal pump operation generally includes a series of the above-described pump cycles.
Bladder pumps have conventionally been controlled by setting the timing for a refill and corresponding discharge cycle. The timing used is generally dependent on the characteristics of the pump, the characteristics of the well, and the objectives to be obtained in operating the pump. For instance, longer periods of injecting compressed air into the bladder are required to lift fluid up through the chamber for greater depths. Similarly, longer periods of venting of the bladder are required for pumps which are submerged to a lesser distance below the water level in the well bore, than for pumps that are located deep within a well bore, or in situations requiring more time to allow the chamber to refill to its full liquid displacement volume.
Furthermore, in recent years, new methods of sampling ground water have come into broader practice. These methods relate primarily to operating the sampling pump at controlled, lower flow rates, so as to provide more accurate samples and produce less purge water. Achieving and reproducing these more precise lower flow rates requires additional skill and care by the operator.
An additional concern in the art of sampling groundwater is excessive drawdown in the well bore. It is important in sampling groundwater with a pump to avoid pumping the water level down to excessive drawdown levels. Otherwise, sample integrity can be compromised. Taking drawdown into account adds another layer of complexity to controlling groundwater sampling pumps.
As a result of this variability in setting and controlling the cycle timing of bladder pumps, conventional methods of pump cycle timing have been difficult to learn and effectively use for some operators. Traditional controllers are operated by manually setting the refill and discharge times to achieve a desired volume per cycle. These adjustments have proven to be complex and difficult for inexperienced pump operators and technicians to master.
Accordingly, it is a principal object of this invention to provide a controller for achieving low, controlled flow rates with fluid pumps, which is easier for experienced and inexperienced operators to adjust than previously available pump controllers. It is an additional purpose of this invention to provide a controller which can be more easily set to control the cycling of a fluid pump to provide an effective means of limiting the amount of water drawdown created in a well in which the pump is disposed.
The above and other objects are provided by a pump controller and method in accordance with preferred embodiments of the present invention.
The method of the present invention includes controlling a cycle time of a pump, such as a well known bladder pump. Additionally, for a given cycle time, the method of the present invention includes controlling the volume of a fluid discharged per cycle by controlling the time within the cycle during which the pump is filled with a compressed fluid such as compressed gas, and subsequently the time allowed for the gas to be vented to the atmosphere. The cycle time, the time during which the pump is filled with compressed gas, and the subsequent time during which the gas is vented from the pump are controlled in response to a user input. It is a principal feature of the controller that these operating parameters can be easily set and modified even by relatively inexperienced technicians or other individuals to achieve desired fluid flow rates.
When the user wishes to increase the volume of the fluid discharged by the pump for a given cycle time, the user causes the controller to generate a signal increasing the time during which the pump discharges fluid, and decreases the time during which the pump refills. The result is a longer period of time during which the pump is filled with compressed air and a shorter period during which the pump is vented. When the user wishes to decrease the volume of the fluid discharged by the pump for a given cycle time, the user causes the controller to generate a signal decreasing the time during which the pump discharges fluid, and increases the time during which the pump refills. The result is a shorter period of time during which the pump is filled with compressed air and a longer period during which the pump is vented. Increasing or decreasing the total amount of fluid discharged by the pump is achieved by adjusting both the cycle time and the fluid volume discharged per cycle simultaneously.
In one embodiment of the present invention, the user interacts with the controller through the use of a control knob or dial and a cycle time input. The control knob is turned in one direction to increase the volume discharged per cycle. The control knob is turned in the opposite direction to decrease the volume discharged per cycle. The cycle time input is used to increase or decrease the cycle time. In another embodiment of the present invention, the user interacts with the controller through the use of an increase-decrease arrow key set and a cycle time input. Pressing an xe2x80x9cincreasexe2x80x9d button increases the volume discharged per cycle and pressing a xe2x80x9cdecreasexe2x80x9d button decreases the volume discharged per cycle. Again, the cycle time input is used to increase or decrease the cycle time.
It is another object of the present invention to provide a controller that temporarily slows or stops pump operation if well drawdown limits are exceeded. To accomplish this, the present invention uses a sensor or probe in communication with the controller to sense the water level. The sensor generates a signal indicating water detection when it makes contact with the water, and correspondingly, stops generating a signal when the sensor is no longer in contact with the water. This signal is propagated to the controller. The controller then adjusts the operation of the pump in response to this signal.
In one mode of operation of the present invention, the controller slows or stops the pump operation in response to a signal indicating that the water level has dropped below the level of the probe. In this mode of operation, the pump remains in the refill mode until the water level rises to the level of the probe. The controller then instructs the pump to resume normal operation in response to a signal indicating that the water level has risen to the level of the probe. In another preferred embodiment, the controller causes the pump to stop and remain inactive for a set period of time in response to a signal that the water level is below the level of the probe. This time delay eliminates a high frequency xe2x80x9cchatterxe2x80x9d that can occur if the state of the water level is such that the signal from the probe repeatedly turns the pump off and on.
In one preferred embodiment of the present invention, the sensor is a conductance probe attached to the end of a measuring tape, which includes wiring for propagating a signal from the probe to the controller. This type of tape is commonly used in the ground water sampling field and includes a hand held revolving reel to store the tape. In conventional use, the probe is lowered into the well. When the probe makes contact with water, the electrical circuitry of the probe senses electrical conductance through the water and propagates a signal to the controller. The probe can also be set to sense an absence of electrical conductance, indicating that the probe is above the water level. In use, the probe is first used to sense the water level in the manner conventionally practiced. The probe is then switched to sense a lack of conductance through water, which allows it to propagate a signal to the controller when the drawdown level is too low. The controller then stops or slows the pump until the water level rises.